Debugging configuration - power / serial/USB cable

I’d like to hookup the serial/USB cable to get some more detailed debugging that is not possible with just printing messages to the cloud. However, my current project uses 800+ LEDs , and with that a 60 amp / 5V power supply that is powering both the LEDs and the Particle.

I worry about now connecting the serial/USB cable into the laptop that there is come potential for that voltage to get into the computer and kill it… I also can’t really disconnect the LED power and just power from the computer for fear that it will then try to power 800+ lights out of the laptop’s power, drawing too much current and frying it.

Not sure if there is a way around this? I’ve looked into a network based debugging/syslog library that may be the solution. Any other ideas/advice?

@davideshay, there is a protection diode between Vusb and the Vin pin that will protect the USB port. If you are concerned, you could use a USB isolator:

or, on Aliexpress

However, I can tell you that no-one has complained of a blown Photon by powering LEDs and the Photon off a large 5V supply to date.

Wasn’t concerned about the Photon at all - built a few of these with similar high-amp configs. But recently when it was powered and I plugged the USB port into my Macbook in order to debug, it came up with a scary message complaining about power on the USB port, so more afraid about blowing up the expensive Macbook than the $30 Photon :smile:

@davideshay, the diode is there to protect the USB connection when the Photon is powered directly via Vin. Perhaps @ScruffR or @BDub can comment on the Macbook message and concerns?

Assuming it was the "To prevent damaging your computer, the USB device drawing too much power has been disabled. Other devices may have also been disabled. When you disconnect the device drawing too much power, your other USB devices will be enabled again,” error, you don’t have to worry. That’s the computer protecting itself by powering down the port that’s drawing too much power. I would avoid doing that, but you won’t damage the computer doing it.

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@rickkas7, that would happen if the USB was plugged in but the power for the LEDs was not turned on I assume? The LEDs would then try to draw current via Vin.

I’m 95% sure that it was powered at the time. I understand that if it wasn’t on, then the mac would be trying to power 800+ LEDs - definitely a problem, but since the other power supply was on, it shouldn’t have been an issue. Also, the LEDs are not powered “through” the Photon, either. They have a separate line from the power supply to them, although they do share a common ground.

I misread the one of the posts. I thought it said plugged in USB without being powered, so in retrospect that message might not be the right one.

@davideshay, the Photon Vin and the power to the LEDs most likely connect to the same point in the power supply.

As @rickkas7 said USB ports on quality devices do have an overcurrent protection which will power down the port before any damage can happen by excessive power draw (e.g. due to a short in the cable/plug/device).
But when you don’t have a scenario that might account for the excessive current draw, you may well have some issues on the cable/connectors or you actually do power something too demanding without being aware of it (e.g. as @peekay123 suggested above).